Mouse embryos contain transforming growth factors (TGFs) that, like those derived from tumor cells, compete with epidermal growth factor for binding to its specific receptor. Utilizing an acid/ethanol extraction technique previously described for the isolation of these factors from tumor cells, these activities have been demonstrated in embryos from six different strains of mice. Two major EGF-competing activities with estimated molecular weights of 10K and 17K have been partially purified from embryo extracts. Both activities support soft agar colony growth in contrast to mouse EGF which is also found, albeit a minor component, in the mouse embryo. TGFs have also been detected in human amniotic fluid and in urine collected from pregnant donors. Both a 17-20K and a 10K EGF competing activity which support soft agar colony growth can be demonstrated in acid-ethanol extracted urine preparations. In addition an 8K variant of EGF which competes for EGF receptors and supports soft agar growth is also found in all urine samples tested including normal donors. Similar TGF activities have also been detected in the urine of a patient with small cell carcinoma of the lung.